1. HIV Immunotherapy
HIV is the focus of intense studies as it is the causative agent for acquired immunodeficiency syndrome (AIDS). Immunotherapeutic methods are one of several approaches to prevention, cure or remediation of HIV infection and HIV-induced diseases. Specifically, the use of neutralizing antibodies in passive immunotherapies is of central importance to the present invention.
Passive immunization of HIV-1 infected humans using human sera containing polyclonal antibodies immunoreactive with HIV has been reported. See for example, Jackson et al., Lancet, Sep. 17: 647-652, (1988); Karpas et al., Proc. Natl. Acad. Sci., USA, 87: 7613-7616 (1990).
Numerous groups have reported the preparation of human monoclonal antibodies that neutralize isolates in vitro. The described antibodies typically have immunospecificities for epitopes on the HIV glycoprotein gp120 or the related external surface envelope glycoprotein gp120 or the transmembrane glycoprotein gp41. See, for example Levy, Micro. Rev., 57: 183-289 (1993); Karwowska et al., Aids Research and Human Retroviruses, 8: 1099-1106 (1992); Takeda et al., J. Clin. Invest., 89: 1952-1957 (1992); Tilley et al., Aids Research and Human Retroviruses, 8: 461-467 (1992); Laman et al., J. Virol., 66: 1823-1831 (1992); Thali et al., J. Virol., 65: 6188-6193 (1991); Ho et al., Proc. Natl. Acad. Sci. USA, 88: 8949-8952 (1991); D'Souza et al., AIDS, 5: 1061-1070 (1991); Tilley et al., Res. Virol., 142: 247-259 (1991); Broliden et al., Immunol., 73: 371-376 (1991); Matour et al., J. Immunol., 146: 4325-4332 (1991); and Gorny et al., Proc. Natl. Acad. Sci., USA, 88: 3238-3242 (1991).
To date, none of the reported human monoclonal antibodies have been shown to be effective in passive immunization therapies. Further, as monoclonal antibodies, they all each react with an individual epitope on the HIV envelope glycoprotein, gp120 or gp160. The epitope against which an effective neutralizing antibody immunoreacts has not been identified.
There continues to be a need to develop human monoclonal antibody preparations with significant HIV neutralization activity. In addition, there is a need for monoclonal antibodies immunoreactive with additional and diverse neutralizing epitopes on HIV gp120 and gp41 in view of recent studies suggesting that gp120 and gp41 are involved in both binding of the HIV virus to the cell as well as in post binding events including envelope shedding and cleavage. See, for review, Levy, Micro. Rev., 57: 183-289 (1993). Additional (new) epitope specificities are required because, upon passive immunization, the administered patient can produce an immune response against the administered antibody, thereby inactivating the particular therapeutic antibody.
2. Human Monoclonal Antibodies Produced From Combinatorial Phagemid Libraries
The use of filamentous phage display vectors, referred to as phagemids, has been repeatedly shown to allow the efficient preparation of large libraries of monoclonal antibodies having diverse and novel immunospecificities. The technology uses a filamentous phage coat protein membrane anchor domain as a means for linking gene-product and gene during the assembly stage of filamentous phage replication, and has been used for the cloning and expression of antibodies from combinatorial libraries. Kang et al., Proc. Natl. Acad. Sci., USA, 88: 4363-4366 (1991). Combinatorial libraries of antibodies have been produced using both the cpVIII membrane anchor (Kang et al., supra) and the cpiii membrane anchor. Barbas et al., Proc. Natl. Acad. Sci., USA, 88: 7978-7982 (1991).
The diversity of a filamentous phage-based combinatorial antibody library can be increased by shuffling of the heavy and light chain genes (Kang et al., Proc. Natl. Acad. Sci., USA, 88: 11120-11123 (1991)), by altering the CDR3 regions of the cloned heavy chain genes of the library (Barbas et al., Proc. Natl. Acad. Sci., USA, 89: 4457-4461 (1992)), and by introducing random mutations into the library by error-prone polymerase chain reactions (PCR) [Gram et al., Proc. Natl. Acad. Sci., USA, 89: 3576-3580 (1992)].
Filamentous phage display vectors have also been utilized to produce human monoclonal antibodies immunoreactive with hepatitis B virus (HBV) or HIV antigens. See, for example Zebedee et al., Proc. Natl. Acad. Sci., USA, 89: 3175-3179 (1992); and Burton et al., Proc. Natl. Acad. Sci., USA, 88: 10134-10137 (1991), respectively. None of the previously described human monoclonal antibodies produced by phagemid vectors that are immunoreactive with HIV have been shown to neutralize HIV.
In particular, none of the previously-described human monoclonal antibodies produced by phagemid vectors are capable of neutralizing a majority of the field isolates of HIV. It is believed that certain of the antibodies described herein are particularly effective at neutralizing HIV because the antibodies immunoreact with an important antigenic determinant present on "mature" gp120 and not present on the HIV precursor protein gp160.